/* 深蓝色#2196f3 亮绿色#02ff02*/
* {
	margin: 0;
	padding: 0;
}
body {
	min-height: 100vh;
	background: black; 
	display: flex;
	justify-content: center;
	align-items: center;
}
a {
	position: relative;
	display: inline-block;
	padding: 1em 2em;
	color: #02ff02;
	letter-spacing: 4px;
	text-decoration: none;
	overflow: hidden;
	transition: .2s;
}
a span {
	position: absolute;
	display: block; 
}
a:hover {
	color: white;
	background: #02ff02;
	box-shadow: 0 0 10px #02ff02,
				0 0 40px #02ff02,
				0 0 80px #02ff02;
	transition-delay: 1.4s;
}
a span:nth-child(1) {
	top: 0;
	left: -100%;
	width: 100%;
	height: 2px;
	background: linear-gradient(90deg,transparent,#02ff02); 
}
a:hover span:nth-child(1) { 
	left: 100%;  
	transition: 1s;
}
a span:nth-child(3) {
	bottom: 0;
	right: -100%;
	width: 100%;
	height: 2px;
	background: linear-gradient(270deg,transparent,#02ff02);
}
a:hover span:nth-child(3) { 
	right: 100%;  
	transition: 1s ;
	transition-delay: .5s;
}
a span:nth-child(2) {
	right: 0;
	top: -100%;
	height: 100%;
	width: 2px;
	background: linear-gradient(transparent,#02ff02);
}
a:hover span:nth-child(2) { 
	top: 100%;  
	transition: 1s ;
	transition-delay: .25s;
}
a span:nth-child(4) {
	left: 0;
	bottom: -100%;
	height: 100%;
	width: 2px;
	background: linear-gradient(#02ff02,transparent);
}
a:hover span:nth-child(4) { 
	bottom: 100%;  
	transition: 1s ;
	transition-delay: .75s;
}